This invention relates to a veneer lathe in which a log is rotated around its longitudinal axis, and a knife contacts the log surface while the log surface adjacent the knife edge is pressed by a pressure member.
According to the prior art for this type of veneer lathe, a log is rotated by a chuck, and a force against the cutting resistance and friction which is due to the pressure member contacting the log surface, is transmitted from the chuck to the cutting surface through the log itself.
This type of veneer lathe has the following drawbacks: First, the veneer lathe cannot be used for logs having a hard structure or for logs soft core section, and including cracks and spoiled sections. This is due to the possibility of the log breaking especially at the core section, and allowing the chuck to freely run, since a large force is applied to the small radius section for transmitting the torque against the cutting resistance at the log surface. Generally, tropical woods, which are now widely used to produce veneer, have a soft core section.
To make matters worse, the log is pressed longitudinally at the chuck so as to ensure the transmission of the torque. The radius of the chuck must be made small in order to cut as much of the log as possible for improved productivity. However, if the chuck is made too small, the risk of breaking the log increases, and thus productivity is limited. Second, wood pieces removed from the log surface often jam between the log and the knife, between the log and the pressure member, and between the knife and the pressure member. Veneer sheets produced under the jam condition are too inferior to be further processed, so consequently material is wasted. Also, when a jam occurs, the log revolving speed must be reduced and often must be stopped completely. This reduces productivity. Furthermore, when a jam occurs, the load increases, frequently resulting in breakage of the log core.
In order to solve these problems, an improved veneer lathe has been disclosed by the same applicant in U.S. patent application Ser. No. 861,278. The veneer lathe proposed in the application is characterized in that drive rollers having sharpened projections on the surface are provided adjacent the knife edge to rotatably drive a log at its circumference, instead of applying the revolving force to the log only through the chuck. In this method, the driving force is applied on the log surface close to the knife edge at several places extending in the longitudinal direction, preventing breakage of the core at the chuck. At the same time, jammed wood pieces can be removed by the driving action of the drive roller.
However, this method has some drawbacks: First, an entire drive roller must be replaced when projections on its surface are broken. Second, the drive rollers thrust the projections on the log surface, and the pressing force against the log when the log diameter becomes small, makes the cutting operation very difficult.